Low Noise Linear Regulator for Power Supply from 200 mA Reference
Low noise power supply with linear regulator IC
For accurate and low noise power supplies, a reference voltage source is typically used, although they are not powering the load. For this type of application, Analog Devices has developed a linear regulator IC with two channels, high channel spacing and precise control.
Developers of analog circuits typically rely on a simple voltage reference to provide low noise voltage to their DA and AD converters. However, this task goes far beyond the reference voltage source - designed to provide a noise-free, accurate and stable voltage to the reference input of the regulator, such as the reference input of a switching regulator in a power converter. Due to certain limitations, the reference voltage source is usually sufficient for the task, encouraging developers to use the reference voltage source to power circuits with higher power requirements. Because if the reference voltage source can power the converter, why not perform analog signal processing or other converters?
The pain of choosing between accuracy and performance often occurs in all development processes. Hauruck recommends using a reference voltage source when accuracy is required and a linear regulator (LDO) when several mW of power is required.
If a source does not meet these two requirements, two must be added and must be on a separate line, even if the nominal voltage is the same. This effort is associated with higher costs and additional space requirements on the board.
Also, if a high precision voltage source is required to provide a few mW of power, the developer must buffer the reference voltage source. ADI's LT6658 solves this problem. It features two low noise precision voltage outputs with an output current of 200 mA. Analog Devices calls him a Refulator and one from the Reference and Regulator.
Low reference voltage drift
The LT6658 is a low noise, low drift precision regulator with a typical voltage reference specification: 10 ppm / K drift with a basic accuracy of 0.05%. The LT6658's two outputs are rated at 150mA and 50mA, respectively, and can also be used as an active absorber. The LT6658 offers higher performance than a linear regulator. To maintain accuracy, the load is controlled to 0.1 ppm / mA. When the input terminals are connected together, the supply voltage penetration is typically 1.4 ppm / V; when the independent source is connected to the input terminals, the supply voltage penetration is less than 0.1 ppm / V.
The typical circuit of the LT6658 consists of a reference voltage source (bandgap), a noise-attenuating filter stage, and two output amplifiers that act as impedance converters and buffer amplifiers. The bandgap reference source and the two output amplifiers are separately powered for extensive decoupling. The inverting input of each output amplifier is taken. This allows the developer to directly feed back the voltage to the load at the input of the amplifier to compensate for the effects of line resistance.
The noise attenuation filter consists of an integrated 400Ω resistor and an external capacitor. It can be used as a low pass filter and limits the noise of the bandgap reference source. The external capacitor can be arbitrarily large, reducing the noise bandwidth to a very low value.